The present invention relates generally to portable motor-driven hammers, and more particularly to an apparatus of this type wherein the hammer-tool holder is spring loaded.
Portable motor-driven hammers and hammer drills are already known. They have a housing in which the tool is journalled, that is a portion of the tool extends into the housing and can slide farther into and farther out of the housing in operation. A rapidly reciprocating strike member is provided in the housing which either strikes the inner end of the tool directly, or strikes an anvil serving to seal the interior of the housing, and which anvil in turn transmits force to the inner end of the tool. In either case, this rapid impacting on the tool causes the desired effect upon the workpiece, for instance upon rock, masonry or the like.
In these constructions the anvil as well as the tool are axially freely movable within certain limits which are determined by appropriate abutments. The movement of the anvil, if one if provided, in the direction towards the handle of the tool, that is the direction where the user holds the tool, is limited by a spring abutment having a spring which is so strongly prestressed that in the case of light-weight hammers the force exerted by the spring is greater than the greatest force with which a user can press the tool of a hammer against a workpiece, and in the case of heavy hammers which are used always in downward direction, the force is greater than the weight of the hammer plus the force exerted by a user. This spring abutment serves to dampen the so-called B-impacts, which tend to vibrate the hammer and be transmitted to the user.
However, there are certain disadvantages involved in these prior-art constructions. The free axial movement of the tool and of the anvil, if one is provided, has the drawback that at the moment at which the impactor impacts the tool or the anvil the tool will frequently not be in contact with the workpiece, and the anvil will not be in contact with the tool. This means that the energy yielded by the impactor upon the anvil directly, or upon the tool directly, is not immediately available for the desired working operation, but is first needed to accelerate the tool, or the anvil plus the tool, in forward direction. This results in longitudinal vibrations of the anvil and the tool which have been observed as using up a significant portion of the energy supplied by the impactor. Evidently, this is undesirable, but heretofore no way has been proposed to overcome this drawback.